install: fix expected log format in gitlog2changelog.py

Update gitlog2changelog.py script to ensure git log format is not
influenced by user git configuration.

Fixes #487.

NEWS.rst

@@ -51,6 +51,8 @@ Modules 5.3.0 (not yet released)
   used with new *fish* shell version (3.6).
 * Install: allow to build Modules from a short-depth git repository. (fix
   issue #486)
+* Install: ensure git log format is not influenced by user's configuration in
+  :command:`gitlog2changelog.py`. (fix issue #487)
 
 
 .. _5.2 release notes:

script/gitlog2changelog.py.in

@@ -14,7 +14,7 @@ if len(sys.argv) > 1:
     rev_range = '%s..HEAD' % base
 
 # Execute git log with the desired command line options.
-fin = os.popen('git log --summary --stat --no-merges --date=short %s' % rev_range, 'r')
+fin = os.popen('git log --pretty=medium --summary --stat --no-merges --date=short %s' % rev_range, 'r')
 # Create a ChangeLog file in the current directory.
 fout = open('ChangeLog', 'w')